1. Field of the Invention
The present invention relates to artificial drying processes, and in particular, to automatically monitoring the moisture content of the material being dried during the drying process.
2. Problems in the Art
Many types of materials must be artificially dried as part of their processing. Some of those materials are porous media. The term xe2x80x9cporous mediaxe2x80x9d, as used herein, means any material that has the ability to retain water, including collections of individual pieces of material, whether or not themselves xe2x80x9cporous mediaxe2x80x9d. By artificial drying, as used herein, it is meant human or machine adjustable application of thermal energy and/or airflow: not a natural application of heat and/or airflow.
A particular example is seed corn. It must be harvested, handled carefully, and usually artificially dried to remove a portion of water it retains. The artificial drying process must be controlled to maintain seed quality, as opposed to non-artificial drying in the natural field environment.
Sometimes this artificial drying is done after the seed has been separated from its carrier, the cob (shelled). Sometimes it is done while the seed corn is still on the cob. In the latter case, ear corn is normally artificially dried in a large bin. It is desirable that the artificial drying removes moisture from the corn down to a certain level at a certain rate. If moisture is removed too quickly, it could damage seed quality. If moisture is removed too slowly, it could also damage seed quality. This can be extremely important. For example, improperly dried seed may not germinate when planted. Thus, it is important to not only monitor drying temperature, but also drying rate and level of moisture in the seed.
One conventional way of such artificial drying of ear corn is to place a relatively large quantity of ear corn (e.g. several tens of bushels) in a relatively large bin (e.g. 125 to 10,000 cubic feet), and manually adjust airflow and temperature of air through the ear corn. Seed corn weighs roughly 85 lbs./ft.3 so there would be thousands of pounds of seed corn in each bin of this size. Normally drying is done simultaneously in multiple such bins. Samples are manually removed periodically and tested for moisture content. Airflow and temperature can then be adjusted to maintain the desired rate of moisture removal. General discussions about the drying of seed corn can be found at: Production of Hybrid Seed Corn, pages 565-607, In: Corn and Corn Improvement 3rd Edition, Edited by G. F. Sprague and J. W. Dudley, Published by the American Society of Agronomy 1988; Physiology of Drying in Maize. J. S. Burris, Pages 1-7, Proceedings of the Seventeenth Annual Seed Technology Conference. Feb. 21, 1995.
Hybrid seed corn is usually artificially dried to allow it to be harvested prior to frost, before being damaged by insects, infected by fungal pathogens, or before the ear falls off the plant. Typically it will take 3 to 4 days for a bin of freshly harvested corn to dry from an initial moisture content of 36% down to a final moisture content of 12%. This rate is determined by the current moisture of seed within a dryer bin, its genotype, and the demand for dryer capacity.
The maximum rate at which seed may be safely dried is determined by the specific drying injury susceptibility of each genotype. If the dryer""s operating conditions are too aggressive, such as too high of temperature or too much airflow, drying injury may occur. These conditions are potentially different for each genotype dried, with harvest moisture interacting with genetic susceptibility in determining ideal drying conditions. Below this maximum rate the seed may be dried at a wide range of possible rates. However, if the dryer""s operating conditions (dryer temperature and airflow) are not properly selected, drying may take an unnecessarily long time, resulting in lost drying capacity and increased energy consumption.
Therefore, two goals are a better final product after artificial drying and more efficient drying. In the case of ear corn, to achieve good levels of efficiency, a relatively large bin is needed to artificially dry a batch of a relatively large amount of ear corn together over a relatively long period of time.
The problem with the above-described method of monitoring drying rate is that it is quite cumbersome. To check on moisture levels of the drying ear corn, samples are periodically manually removed from the dryer bin and known laboratory techniques used to derive moisture content of the corn sample. A worker must physically gain entrance to the drying chamber (e.g. through a door) and manually extract one or more sample ears. Some bins are large enough that the worker can substantially enter the bin and grab ears of corn. Others have doors or access openings big enough for the worker to reach into the corn. However, in most cases, the worker can only reach a few feet deep into the pile of corn (e.g. up to his/her elbow) and extract an ear or two. If the ear is grabbed from near the top of the pile, the top is many times the last part of the pile to dry (if heated air is supplied from the bottom). Therefore, ears extracted from the top may not accurately characterize moisture content of the majority of the pile. Thus, many times the worker extracts ears from several places in the pile (e.g. 8 to 10 ears). This greatly increases the manual work involved.
The worker must then remove some seed from each extracted ear (again usually manually). The removed seed must then be manually handled and loaded into a machine or device for analysis (usually by laboratory-type moisture measuring equipment). After the results are obtained (normally after a period of time and not in real time), they can then be used to evaluate the drying process and/or to control the drying process. Many times this means the worker must key the moisture data into a computer.
Not only is the above-described process time-consuming, cumbersome, and labor intensive (drying usually proceeds over several days with moisture measures taken several times each day), it is difficult, if not impossible, to remove actual samples from very deep in the bin. Therefore, it is difficult to really test how drying is proceeding throughout the bin. Moisture readings from ear corn taken from the top, bottom, or a side of the bin may not be accurate for other locations in the bin, such as the middle of the bin. Such readings may mislead and cause application of a moisture removal rate detrimental to the corn. Furthermore, this process is subject to operator errors and accuracy problems. These problems are amplified because typically 72 to 96 dryer bins are run simultaneously to artificially dry a plurality of batches of relatively large amounts of corn.
There have been attempts to automate the drying process. For example, see U.S. Pat. No. 5,893,218 to inventors Hunter, Precetti and Chicoine, incorporated by reference herein. That patent discloses a system that makes it easier to control airflow rate and temperature in such relatively large dryer bins. But it relies on known moisture measuring methods, such as described above.
Therefore, it would be very helpful to also have automated measurement of moisture content or monitoring of drying rate of the ear corn in essentially real-time during the drying process. This intelligence could be used to monitor artificial drying and/or be used by an automated artificial drying apparatus to control the drying process.
Attempts have been made to create devices to measure moisture in porous media, including shelled corn or ear corn. One such example is the use of a radioactive source (e.g. neutron probe). A major problem with such a detector is that it creates safety issues for workers. It also requires special licensing and administrative burdens that are not insubstantial.
Another attempt uses a capacitance probe. Its primary deficiency is that it can only measure moisture near the bottom of the bin.
Microwave instruments, on the order of 1xe2x80x2xc3x971xe2x80x2, have been used. However, they cannot be used for substantial-sized dryer bins such as are used with ear corn or other bulk products.
Many of the above-described methods can sense or derive moisture content from just a small volume of material (e.g. one to a few seed or ears of corn). Therefore, they are not conducive to monitoring large volumes, such as in the example of ear corn drying discussed above.
In part because of the lack of a satisfactory measurement apparatus or method, sometimes predictions are used for moisture content, however, such predictions can be very inaccurate.
A methodology called time domain reflectometry (TDR) has been utilized to test electrical cables for breaks or defects. A electromagnetic pulse is sent down a cable. The location of a discontinuity (e.g. break) in the cable can be derived. The break will cause the pulse to be reflected back to source. Because the speed of the pulse is known, by timing the pulse and its reflection from a known starting point, the distance from the starting point to the break can be calculated.
Time domain reflectometry has also been used to attempt to sense moisture levels in the soil. In the case of soil, a relatively small probe (e.g. 20 cm long, xe2x85x9xe2x80x3 diameter rod(s)) is inserted into the soil. A portable processor instructs the generation of an electromagnetic pulse. Reflections of the pulse from the probe ends are evaluated and moisture content of the soil around the probe is derived. A basic discussion of TDR can be found at White, I., Zegelin, S. J., Topp, G. C., and Fish, A, xe2x80x9cEffect of Bulk Electrical Conductivity on TDR Measurement of Water Content in Porous Mediaxe2x80x9d, published in Symposium and Workshop on Time Domain Reflectometry in Environmental, Infrastructure, and Mining Applications, Northwestern University, Evanston, Ill., Sep. 17-19, 1994 (Washington, D.C.: U.S. Bureau of Mines, 1994), pp. 294-308, USBM special publication SP 19-94, which is incorporated by reference herein.
Further reference can be taken to Soilmoisture Equipment Corporation Operating Instructions for Model 6050X1 Trase System I, available from Soilmoisture Equipment Corp., 801 S. Kellogg Ave., Goleta, Calif. 93117, also incorporated by reference herein. Principles and techniques of operation for use of Model 6050X1 for TDR measurement of moisture in soil is set forth.
TDR is based on the fact that propagation velocity of an electromagnetic wave along a transmission line (or waveguide) embedded in a material can be determined from the time response of a system to an electromagnetic pulse that becomes the wave, coupled with the fact that propagation velocity is a function of the bulk dielectric constant of the material in which the waveguide carrying the wave is embedded. Generally, the dielectric of a material is the ratio squared of propagation velocity in a vacuum relative to that in the material. If the bulk dielectric of the material, as it is with soil, is essentially governed by the dielectric of liquid water contained in the material, TDR is relatively insensitive to the composition of the non-liquid water components of the material. Such also is the case with seed corn and ear corn (e.g. bulk dielectric for unbound water is approximately 80; for corn approximately 1, whether ear corn or seed corn).
Essential to an understanding of the use of TDR to measure moisture of a material is the fact that although the electromagnetic pulse is sent through a transmission line such as an electrically conductive probe inserted in the material, its time of travel is affected primarily by the material around the probe, if there is substantial water content in the material. As surface waves (TEM or transverse electromagnetic waves) propagate along the probe inserted in the material being measured, the signal envelope is attenuated in proportion to the electrical conductivity along the travel path. This electrical conductivity is affected by the dielectric constant of the material around the probe. Thus, there is a proportional reduction in signal velocity. By measuring signal velocity, dielectric constant of the material can be calculated and by calibration with measurements taken from material of known moisture content, a calibration curve or relationship can be created to derive percent moisture content, because of the known relationship between dielectric constant and percent moisture content. See, e.g., Evett, S. R., xe2x80x9cCoaxial Multiplexer for Time Domain Reflectometry Measurement of Soil Water Content and Bulk Electrical Conductivityxe2x80x9d Transactions of the American Society of Agricultural Engineers (ASAE), Vol. 41(2):361-369, incorporated by reference herein. See also, Irrigation of Agricultural Crops, Number 30 in the series AGRONOMY, Published by the American Society of Agronomy 1990; and Time-domain Reflectometry for Measuring Water Content of Organic Growing Media in Containers. Tomaz Anisko, D. Scott NeSmith, and Orville M. Lindstrom. HortScience 29(12):1511-1513.1994, both incorporated by reference herein.
U.S. Pat. No. 5,376,888 to Hook, incorporated by reference herein, discloses a TDR system with probes insertable into material undergoing test for water or other liquid content, including granular and/or particulate materials other than soil, sand, or the like, giving grain and alcohol as examples, and is incorporated by reference herein in its entirety, including its discussion of the operation of TDR. However, Hook""s methodology is not what is normally done in TDR waveform analysis. Hook""s methods lose significant waveform information by the shorting methods disclosed. Hook therefore explains the principle of TDR in that context. A stepped pulse is generated and sent down the waveguide or probe. The reflection is analyzed to derive velocity of propagation of the wave by timing the wave through the probe and back. From the velocity of propagation, dielectric constant Ka can be derived. From Ka, volumetric water content can be derived. U.S. Pat. No. 5,376,888 is primarily concerned with making the beginning and end of the waveguide probe more clearly discriminated in the signal for increased accuracy of timing measurement points. It discloses 0.125xe2x80x3 diameter stainless steel rods for the waveguide, similar to the size and configuration of TDR soil sample waveguides. Thus, such an apparatus can be used to quickly and easily measure moisture by inserting a small probe into the soil.
Hook""s purposeful xe2x80x9cshortingxe2x80x9d is believed to be intended to produce a very distinctive end point reflection that did not need much interpretation or tangent fitting to derive an endpoint. The waveform is not like that created and observed in a step pulse (non-shorted) TDR system, such as the preferred embodiment of the present invention, and described in such literature as the previously mentioned Topp article and by others relative to determination of endpoint reflections used in TDR for determination of moisture content in a complex porous material such as soil, seeds or similar material. Hook""s methods are particular to the instruments built by Hook and are not the accepted normal method of accurately determining water content by TDR methods. A shorted signal, such as in Hook, produces a flat line until the end reflection thereby eliminating important impedance information in the waveform as the electromagnetic pulse travels the waveguides. The impedance levels provide information as to the consistency of the material being measured along the path of the pulse. The delta t travel time (from beginning to end along a probe(s)) provides the average speed of propagation and therefore moisture content can be derived. The impedance along that traveled probe path changes along the path and provides some indication of the material""s uniformity along the path of the probe. This can be very helpful in managing the drying of substances such as corn using long probes where one would like to know uniformity and deviations.
However, no time domain reflectometry (TDR) system is known which has been applied either to measuring moisture in porous media such as a batch of agricultural product such as ear corn for the purpose of monitoring moisture level or drying rate of a porous media during an artificial drying process.
There is a need in the art for an apparatus and method of autonomously monitoring of drying of agricultural porous media such as grain or seed that does not have the danger and licensing requirements of radioactive sources, allows essentially real time measurements, is non-destructive, allows use of a probe or probes sized for and operable in relatively large dryer bins, and is relatively inexpensive and durable. The need in the art includes the need for automatic non-destructive measurements that are sufficiently accurate for monitoring the drying process from a relevant location or locations in the material being artificially dried in the relatively large bins. The need also includes minimum interference with normal drying of the material. For example, there optimally would be a minimum decrease in the volume of drying space available, a minimum disruption of or interference with the flow of drying air and/or heat into, through, and out of the material; and minimum influence on the natural packing of material in the drying chamber. The need also includes robustness and durability for each particular environment and material; in one example, the forces caused by thousands of pounds of ear corn when loaded into a dryer bin, dried there, and then removed. Also, it is preferable that the apparatus and method have minimum affect on contamination of a succeeding batch of material from a preceding batch. Ideally, the system should be substantially self-cleaning, so that material from one batch does not remain when that batch is unloaded by normal methods, and additional cleaning steps are not usually required. Furthermore, there is need to minimize physical access by a worker inside of a dryer bin. OSHA regulations are fairly strict on this point. It would be desirable to eliminate or reduce the need for a worker to enter or even reach into the bins.
Objects, Features, or Advantages of Some Embodiments of the Invention
It is therefore a principal object, feature, or advantage of the present invention to provide an apparatus and method for monitoring drying of a porous media that improves over the problems and deficiencies in the art.
Other objects, features or advantages of certain embodiments of the invention include an apparatus or method as above described that:
a. provides for improved drying control;
b. provides for good quality final product after drying;
c. provides for automated drying;
d. provides for essentially real time moisture monitoring, even for relatively large amounts of porous media;
e. optionally provides for moisture readings at a variety of locations throughout the porous media, including rapid sequential readings from various locations in the product to be dried;
f. is relatively inexpensive, economical, and efficient;
g. is durable and long lasting;
h. provides for more efficient use of drying equipment;
i. provides for good level of accuracy;
j. is non-destructive and does not require alteration of the material being dried;
k. bases monitoring on actual measures not predictions;
l. does not have unduly complex or difficult calibration requirements;
m. is not necessarily product-specific relative to the product being dried;
n. avoids safety hazards that exist with other methods;
o. provides a significant amount of flexibility regarding location, orientation, and use of the measurement apparatus and the information derived therefrom;
n. provides for good spatial and temporal resolution;
p. provides for continuous data gathering;
q. is substantially self-cleaning;
r. presents minimal interference with the drying process; and
s. presents minimal disruption of normal packing of material in the drying chamber.
These and other objects, features, or advantages of the present invention or embodiments thereof will become more apparent with reference to the accompanying specification and claims.
The present invention is an apparatus and method for monitoring drying of an agricultural porous media such as grain or seed. The method according to the invention includes deriving moisture content using time domain reflectometry and utilizing the derived moisture content to monitor drying of the porous media. An optional feature of the method is deriving moisture content at a variety of locations throughout the porous media and utilizing those readings to monitor drying of the porous media. A further possible feature of the method is to utilize derived moisture content to control an artificial drying process.
The apparatus according to the invention includes a drying chamber for holding a porous media to be dried, a time domain reflectometry probe adapted for placement in a selected position in the drying chamber; and a time domain reflectometry device electrically connected to the probe and adapted to derive moisture content of the porous media. A possible feature of the apparatus is an array of probes positioned in different places in the drying chamber to collect moisture data at different locations in the porous media during drying. Another possible feature is to electrically connect the data output from the TDR device to another device, such as a computer and/or an automated artificial drying controller which controls the drying process for the drying chamber. Furthermore, one or more TDR probes could be placed in a plurality of drying chambers for moisture monitoring and/or control in each chamber.